It's a well-known fact that stress can weaken the immune system. In
this study, the researchers sought to determine whether hugs - like social support more broadly - could protect individuals from the increased susceptibility to
illness brought on by the particular stress that comes with
interpersonal conflict.

"We tested whether perceptions of social support are equally effective
in protecting us from stress-induced susceptibility to infection and
also whether receiving hugs might partially account for those feelings
of support and themselves protect a person against infection."

In the experiment, over 400 healthy adults who filled out a
questionnaire about their perceived social support and also participated
in a nightly phone interview for two weeks. They were asked about the
frequency that they engaged in interpersonal conflict and received hugs
that day.

Then, the researchers exposed the participants to a common cold
virus, and monitored them to assess signs of infection. They found that
both perceived social support and more frequent hugs reduced the risk of
infection associated with experiencing interpersonal conflict.

Regardless of whether or not they experienced social conflicts, infected
participants with greater perceived social support and more frequent
hugs had less severe illness symptoms.

"This suggests that being hugged by a trusted person may act as an
effective means of conveying support and that increasing the frequency
of hugs might be an effective means of reducing the deleterious effects
of stress," Cohen said.

"The apparent protective effect of hugs may be attributable to the
physical contact itself or to hugging being a behavioral indicator of
support and intimacy ... either way, those who receive more hugs are
somewhat more protected from infection."